Comments

On Wed, Jan 23, 2013 at 12:06:40PM +0100, Hannes Frederic Sowa wrote:
> On Wed, Jan 23, 2013 at 12:05:16PM +0200, Michael S. Tsirkin wrote:> > This is when trying to start a VPN using some old openvpn binary so MQ> > is not set.> > > > So> > 1. I think we should limit allocation of MQ to when MQ flag is set in SETIFF.> > 2. order 7 allocation is 2^^7 pages - about half a megabyte of contigious> > memory. This is quite likely to fail.> > Let's start with a small limit on number of queues, like 8?> > Then we know it will succeed.> > Longer term we might want to solve it differently.> > This has been come up before:> http://thread.gmane.org/gmane.linux.network/255647/focus=255902> > I think a solution to this problem is still outstanding.
Right. What (at least I) missed is that it's the
queue array allocation that fails here.
So I think something like the following will sort the first issue
(compiled only):
For the second, for 3.8 maybe the prudent thing to do is
to set MAX_TAP_QUEUES to a small value, like 8, to avoid
userspace relying on a large number of queues being available,
and look at a better way to do this longer term, like
using an array of pointers.
--->
tun: don't waste memory on unused queues
If MQ flag is off, we never attach more than 1 queue.
So let's not allocate memory for the unused ones.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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On 01/23/2013 07:41 PM, Michael S. Tsirkin wrote:
> On Wed, Jan 23, 2013 at 12:06:40PM +0100, Hannes Frederic Sowa wrote:>> On Wed, Jan 23, 2013 at 12:05:16PM +0200, Michael S. Tsirkin wrote:>>> This is when trying to start a VPN using some old openvpn binary so MQ>>> is not set.>>>>>> So>>> 1. I think we should limit allocation of MQ to when MQ flag is set in SETIFF.>>> 2. order 7 allocation is 2^^7 pages - about half a megabyte of contigious>>> memory. This is quite likely to fail.>>> Let's start with a small limit on number of queues, like 8?>>> Then we know it will succeed.>>> Longer term we might want to solve it differently.>> This has been come up before:>> http://thread.gmane.org/gmane.linux.network/255647/focus=255902>>>> I think a solution to this problem is still outstanding.> Right. What (at least I) missed is that it's the> queue array allocation that fails here.> So I think something like the following will sort the first issue> (compiled only):>> For the second, for 3.8 maybe the prudent thing to do is> to set MAX_TAP_QUEUES to a small value, like 8, to avoid> userspace relying on a large number of queues being available,> and look at a better way to do this longer term, like> using an array of pointers.
Sure, this is just the method I reply in that thread. Not sure 8 is the
best, but since it fit into one page, should be ok. Maybe we can use
flex array to avoid high order memory allocation in the longer term.
>> --->>> tun: don't waste memory on unused queues>> If MQ flag is off, we never attach more than 1 queue.> So let's not allocate memory for the unused ones.>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>>> --->> diff --git a/drivers/net/tun.c b/drivers/net/tun.c> index af372d0..813d303 100644> --- a/drivers/net/tun.c> +++ b/drivers/net/tun.c> @@ -1577,6 +1577,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)> else {> char *name;> unsigned long flags = 0;> + unsigned int max_tap_queues;> > if (!ns_capable(net->user_ns, CAP_NET_ADMIN))> return -EPERM;> @@ -1599,9 +1600,13 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)> if (*ifr->ifr_name)> name = ifr->ifr_name;> > + if (ifr->ifr_flags & IFF_MULTI_QUEUE)> + max_tap_queues = MAX_TAP_QUEUES;> + else> + max_tap_queues = 1;> dev = alloc_netdev_mqs(sizeof(struct tun_struct), name,> tun_setup,> - MAX_TAP_QUEUES, MAX_TAP_QUEUES);> + max_tap_queues, max_tap_queues);> if (!dev)> return -ENOMEM;>
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